1. Field of the Invention
The present invention relates to a semiconductor acceleration sensor for use in, for example, an automotive ABS (anti-lock braking system), air-bag system, suspension system and so forth.
2. Description of the Related Art
FIG. 5 is a perspective view of a conventional acceleration sensor. Referring to this Figure, an acceleration sensing beam 3 is provided with gauge resistors 1a to 1d each capable of converting mechanical stress into an electrical signal by piezoelectric resistance effect. These gauge resistors 1a to 1d are electrically connected so as to form a bridge circuit which is not shown. The reverse side of the acceleration sensor beam 3, opposite to the side where the gauge resistors 1a to 1d are formed, is partly thin-walled so as to provide a diaphragm 2.
The acceleration sensor beam 3 is cantilevered by a pedestal 4 which in turn is fixed to a base substrate 5. Lead pins 6 for transmitting electrical signals from the acceleration sensor beam 3 to the exterior of the sensor are provided on the base substrate 5. The lead pins 6 are electrically connected to the acceleration sensor beam 3 through wires 7. Although not shown, a cap is provided on the base substrate 5 so as to cover the acceleration sensor beam 3.
In operation of the conventional semiconductor acceleration sensor having the described construction, acceleration is applied to the sensor in a direction perpendicular to the major surface of the base substrate shown in FIG. 5, so that the acceleration sensor beam 3 is deflected by an amount corresponding to the magnitude of the acceleration. As a result of the deflection of the acceleration sensor beam 3, electrical resistances are changed in the resistors 1a to 1d, and an electromotive force is generated in the bridge circuit so as to indicate the magnitude of the acceleration.
The conventional acceleration sensor of the type described suffers from a disadvantage in that acceleration is detectable only in the direction perpendicular to the base substrate 5. Therefore, a suspension system which is required to operate in response to accelerations acting in two or three directions essentially necessitate two or three semiconductor acceleration sensors, resulting in an increase in the number of parts employed.